In prosthodontic procedures designed to implant a dental prosthesis in the oral cavity, the dental site at which the prosthesis is to be implanted in many cases should be measured accurately and studied carefully, so that a prosthesis such as a crown, denture or bridge, for example, can be properly designed and dimensioned to fit in place. A good fit enables mechanical stresses to be properly transmitted between the prosthesis and the jaw, and to prevent infection of the gums via the interface between the prosthesis and the dental site, for example.
Some procedures also call for removable prosthetics to be fabricated to replace one or more missing teeth, such as a partial or full denture, in which case the surface contours of the areas where the teeth are missing need to be reproduced accurately so that the resulting prosthetic fits over the edentulous region with even pressure on the soft tissues.
In some practices, the dental site is prepared by a dental practitioner, and a positive physical model of the dental site is constructed using known methods. Alternatively, the dental site may be scanned to provide 3D data of the dental site. In either case, the virtual or real model of the dental site is sent to the dental lab, which manufactures the prosthesis based on the model. However, if the model is deficient or undefined in certain areas, or if the preparation was not optimally configured for receiving the prosthesis, the design of the prosthesis may be less than optimal. For example, if the insertion path implied by the preparation for a closely-fitting coping would result in the prosthesis colliding with adjacent teeth, the coping geometry has to be altered to avoid the collision, which may result in the coping design being less optimal. Further, if the area of the preparation containing a finish line lacks definition, it may not be possible to properly determine the finish line and thus the lower edge of the coping may not be properly designed. Indeed, in some circumstances, the model is rejected and the dental practitioner then re-scans the dental site, or reworks the preparation, so that a suitable prosthesis may be produced.
In orthodontic procedures it can be important to provide a model of one or both jaws. Where such orthodontic procedures are designed virtually, a virtual model of the oral cavity is also beneficial. Such a virtual model may be obtained by scanning the oral cavity directly, or by producing a physical model of the dentition, and then scanning the model with a suitable scanner.
Thus, in both prosthodontic and orthodontic procedures, obtaining a three-dimensional (3D) model of a dental site in the oral cavity is an initial procedure that is performed. When the 3D model is a virtual model, the more complete and accurate the scans of the dental site are, the higher the quality of the virtual model, and thus the greater the ability to design an optimal prosthesis or orthodontic treatment appliance(s).
Scanning of the dental site is complicated by regions in which a patient is missing teeth, referred to as edentulous regions. For example, in cases where two or more adjacent teeth are missing, there may be a large span of soft tissue that needs to be scanned. Such regions can be difficult to scan.
Some intraoral scanners are used in conjunction with a powder that is applied to a dental region. The powder may include particles that reflect light, with the goal of providing measurable points in the dental site. For such systems, these particles may be used to aid image registration when they operate as intended. However, the powder often does not connect well to soft tissue, and in particular to wet soft tissue. Additionally, the powder may become wet and/or wash away during scanning, decreasing an accuracy of later image registration. Additionally, many patients do not like having the powder applied to their teeth and in their mouth. Having to powder the teeth can have drawbacks such as:    1. All areas have to be powdered and the thickness of the powder layer is not homogeneous, which compromises accuracy (e.g., since the surface is not scanned directly);    2. If the scanner head touches the powder, it sticks to the optics and introduces noise to the scan;    3. The powder can be costly;    4. Some people are allergic to the powder; and    5. Color scanning of the teeth is not possible as it is all painted in white.